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MA: Fachverband Magnetismus

MA 7: ThyssenKrupp Electrical Steel Dissertationspreis der AG Magnetismus

MA 7.1: Vortrag

Montag, 31. März 2014, 12:30–12:50, HSZ 04

Spin Polarization, Circular Dichroism and Robustness of Topological Surface States — •Markus R. Scholz — Helmholtz-Zentrum Berlin

Three dimensional topological insulators are characterized by an insulating bulk and a surface that hosts robustly metallic surface states. By means of spin and angle-resolved photoemission we demonstrate that the topological surface state of Bi2Te3 is highly spin polarized as expected from theory. However, the polarization remains finite owing to the strong spin-orbit coupling present in these systems.

We further investigate the influence of time-reversal-symmetry breaking ferromagnetic impurities on the surface state dispersion of Bi2Se3 and Bi2Te3. We find that, in contrast to current belief, the topological surface state survives even a massive deposition of Fe impurities and remains gapless. An analysis of the photoemission line widths, however, shows that the ferromagnetic impurities have a much stronger influence on the decay of photoholes than non-magnetic impurities. Moreover, we have analyzed the influence of the spin-vector orientation on the scattering rates which leads to a strong asymmetry in the scattering rates for the different high symmetry directions in k-space.

Finally, we have uncovered a strong circular dichroism in the angle distribution of photoelectrons in Bi2Te3. By photon-energy dependent studies we have revealed a sign change of the dichroism effect. With the help of one-step-photoemission calculations we were able to show that this sign change rules out ground-state models given as an explanation for this effect in the literature, and that, hence, the circular dichroism is not a measure of the spin polarization in the initial state of the photoemission transition.